Fuel cell cathodes and their fuel cells

ABSTRACT

Fuel cell cathodes and instant startup fuel cells employing the cathodes. The cathodes operate through the valency change mechanism of redox couples which uniquely provide multiple degrees of freedom in selecting the operating voltages available for such fuel cells. Such cathodes provide the fuel cells in which they are used a “buffer” or “charge” of oxidizer available within the cathode at all times.

RELATED APPLICATIONS

The present invention is a continuation-in-part of U.S. patentapplication Ser. No. 10/185,414, which is assigned to the same assigneeas the current application, entitled “FUEL CELL CATHODE WITH REDOXCOUPLE”, filed Jun. 28, 2002, now U.S. Pat. No. 6,777,125 which is acontinuation-in-part of U.S. patent application Ser. No. 09/797,332,which is assigned to the same assignee as the current application,entitled “Novel Fuel Cell Cathodes and Their Fuel Cells”, filed Mar. 1,2001, now U.S. Pat. No. 6,620,539, the disclosure of which is herebyincorporated by reference.

FIELD OF THE INVENTION

The instant invention relates to generally to useful cathodes activematerials for fuel cells, more specifically to their use as the cathodematerial for instant startup alkaline fuel cells. These inventivecathodes open up a tremendous number of degrees of freedom in fuel celldesign by utilizing the change in valency states via reduction/oxidationof the cathode active material.

BACKGROUND OF THE INVENTION

The instant application for the first time provides cathodes, and fuelcells using such electrodes, which use oxide couples to yield a wideselection of operating voltages. Specifically, the instant inventorshave determined materials, when used in combination with hydrogenelectrodes including hydrogen storage material, yield high performancefuel cells. The high performance fuel cells have hydrogen storagecapacity within the hydrogen electrode and cathodes which take advantageof low-cost, in comparison with the traditional platinum electrodes,oxide couples which allow selection of specific ranges of operatingvoltage of the electrochemical cells with a broad operating temperaturerange and the opportunity to provide instant-start by use of thehydrogen storage capability of the short-range order available in thematerial of the hydrogen electrode.

As the world's human population expands, greater amounts of energy arenecessary to provide the economic growth all nations desire. Thetraditional sources of energy are the fossil fuels which, when consumed,create significant amounts of carbon dioxide as well as other moreimmediately toxic materials including carbon monoxide, sulfur oxides,and nitrogen oxides. Increasing atmospheric concentrations of carbondioxide are warming the earth; creating the ugly specter of globalclimatic changes. Energy-producing devices which do not contribute tosuch difficulties are needed now.

A fuel cell is an energy-conversion device that directly converts theenergy of a supplied gas into an electric energy. Highly efficient fuelcells employing hydrogen, particularly with their simple combustionproduct of water, would seem an ideal alternative to current typicalpower generations means. Researchers have been actively studying suchdevices to utilize the fuel cell's potential high energy-generationefficiency.

The base unit of the fuel cell is a cell having a cathode, an anode, andan appropriate electrolyte. Fuel cells have many potential applicationssuch as supplying power for transportation vehicles, replacing steamturbines and power supply applications of all sorts. Despite theirseeming simplicity, many problems have prevented the widespread usage offuel cells.

Presently most of the fuel cell R & D is focused on P.E.M. (ProtonExchange Membrane) fuel cells. Regrettably, the P.E.M. fuel cell suffersfrom relatively low conversion efficiency and has many otherdisadvantages. For instance, the electrolyte for the system is acidic.Thus, noble metal catalysts are the only useful active materials for theelectrodes of the system. Unfortunately, not only are the noble metalscostly, they are also susceptible to poisoning by many gases,specifically carbon monoxide (CO). Also, because of the acidic nature ofthe P.E.M fuel cell electrolyte, the remainder of the materials ofconstruction of the fuel cell need to be compatible with such anenvironment, which again adds to the cost thereof. The proton exchangemembrane itself is quite expensive, and because of it's low protonconductivity at temperatures below 80° C., inherently limits the powerperformance and operational temperature range of the P.E.M. fuel cell asthe PEM is nearly non-functional at low temperatures. Also, the membraneis sensitive to high temperatures, and begins to soften at 120° C. Themembrane's conductivity depends on water and dries out at highertemperatures, thus causing cell failure. Therefore, there are manydisadvantages to the P.E.M. fuel cell which make it somewhat undesirablefor commercial/consumer use.

The conventional alkaline fuel cell has some advantages over P.E.M.fuels cells in that they have higher operating efficiencies, they useless costly materials of construction, and they have no need forexpensive membranes. The alkaline fuel cell also has relatively higherionic conductivity in the electrolyte, therefore it has a much higherpower capability. While the conventional alkaline fuel cell is lesssensitive to temperature than the PEM fuel cell, the platinum activematerials of conventional alkaline fuel cell electrodes become veryinefficient at low temperatures. Unfortunately, conventional alkalinefuel cells still suffer from their own disadvantages.

For example, conventional alkaline fuel cells still use expensive noblemetal catalysts in both electrodes, which, as in the P.E.M. fuel cell,are susceptible to gaseous contaminant poisoning. The conventionalalkaline fuel cell is also susceptible to the formation of carbonatesfrom CO₂ produced by oxidation of the anode carbon substrates orintroduced via impurities in the fuel and air used at the electrodes.This carbonate formation clogs the electrolyte/electrode surface andreduces/eliminates the activity thereof. The invention described hereineliminates this problem from the anode.

Fuel cells, like batteries, operate by utilizing electrochemicalreactions. Unlike a battery, in which chemical energy is stored withinthe cell, fuel cells generally are supplied with reactants from outsidethe cell. Barring failure of the electrodes, as long as the fuel,preferably hydrogen, and oxidant, typically air or oxygen, are suppliedand the reaction products are removed, the cell continues to operate.

Fuel cells offer a number of important advantages over internalcombustion engine or generator systems. These include relatively highefficiency, environmentally clean operation especially when utilizinghydrogen as a fuel, high reliability, few moving parts, and quietoperation. Fuel cells potentially are more efficient than otherconventional power sources based upon the Carnot cycle.

The major components of a typical fuel cell are the anode for hydrogenoxidation and the cathode for oxygen reduction, both being positioned ina cell containing an electrolyte (such as an alkaline electrolyticsolution). Typically, the reactants, such as hydrogen and oxygen, arerespectively fed through a porous anode and cathode and brought intosurface contact with the electrolytic solution. The particular materialsutilized for the cathode and anode are important since they must act asefficient catalysts for the reactions taking place.

In an alkaline fuel cell, the reaction at the anode occurs between thehydrogen fuel and hydroxyl ions (OH⁻) present in the electrolyte, whichreact to form water and release electrons:H₂+2OH⁻→2H₂O+2e ⁻ E ₀=−0.828 v.At the cathode, the oxygen, water, and electrons react in the presenceof the cathode catalyst to reduce the oxygen and form hydroxyl ions(OH⁻):O₂+2H₂O+4e ⁻→4OH⁻ E ₀=−0.401 v.The total reaction, therefore, is:2H₂=O₂→2 2H₂O E ₀=−1.229 vThe flow of electrons is utilized to provide electrical energy for aload externally connected to the anode and cathode.

It should be noted that the anode catalyst of the alkaline fuel cell isrequired to do more than catalyze the reaction of H⁺ ions with OH⁻ ionsto produce water. Initially the anode must catalyze and accelerate theformation of H⁺ ions and e⁻ from H₂. This occurs via formation of atomichydrogen from molecular hydrogen. The overall reaction may be simplifiedand presented (where M is the catalyst) as:

M+H₂→2M . . . H→M+2H⁺+2e ⁻.

Thus the anode catalyst must not only efficiently catalyze theelectrochemical reaction for formation of water at the electrolyteinterface but must also efficiently dissociate molecular hydrogen intoatomic hydrogen. Using conventional anode material, the dissociatedhydrogen is transitional and the hydrogen atoms can easily recombine toform hydrogen if they are not used very efficiently in the oxidationreaction. With the hydrogen storage anode materials of the inventiveinstant startup fuel cells, hydrogen is stored in hydride form as soonas they are created, and then are used as needed to provide power.

In addition to being catalytically efficient on both interfaces, thecatalytic material must be resistant to corrosion by the alkalineelectrolyte. Without such corrosion resistance, the electrode wouldquickly succumb to the harsh environment and the cell would quickly loseefficiency and die.

One prior art fuel cell anode catalyst is platinum. Platinum, despiteits good catalytic properties, is not very suitable for wide scalecommercial use as a catalyst for fuel cell anodes, because of its veryhigh cost, availability, and the limited world supply. Also, noble metalcatalysts like platinum, also cannot withstand contamination byimpurities normally contained in the hydrogen fuel stream. Theseimpurities can include carbon monoxide which may be present in hydrogenfuel or contaminants contained in the electrolyte such as the impuritiesnormally contained in untreated water including calcium, magnesium,iron, and copper.

The above contaminants can cause what is commonly referred to as a“poisoning” effect. Poisoning occurs where the catalytically activesites of the material become inactivated by poisonous species invariablycontained in the fuel cell. Once the catalytically active sites areinactivated, they are no longer available for acting as catalysts forefficient hydrogen oxidation reaction at the anode. The catalyticefficiency of the anode therefore is reduced since the overall number ofavailable catalytically active sites is significantly lowered bypoisoning. In addition, the decrease in catalytic activity results inincreased over-voltage at the anode and hence the cell is much lessefficient adding significantly to the operating costs. Overvoltage isthe difference between the actual working electrode potential under someconditions and it's equilibrium value, the physical meaning ofovervoltage is the voltage required to overcome the resistance to thepassage of current at the surface of the anode (charge transferresistance). The overvoltage represents an undesirable energy loss whichadds to the operating costs of the fuel cell.

In related work, U.S. Pat. No. 4,623,597 (“the '597 patent”) and othersin it's lineage, the disclosure of which is hereby incorporated byreference, one of the present inventors, Stanford R. Ovshinsky,described disordered multi-component hydrogen storage materials for useas negative electrodes in electrochemical cells for the first time. Inthis patent, Ovshinsky describes how disordered materials can be tailormade (i.e., atomically engineered) to greatly increase hydrogen storageand reversibility characteristics. Such disordered materials areamorphous, microcrystalline, intermediate range order, and/orpolycrystalline (lacking long range compositional order) wherein thepolycrystalline material includes topological, compositional,translational, and positional modification and disorder. The frameworkof active materials of these disordered materials consist of a hostmatrix of one or more elements and modifiers incorporated into this hostmatrix. The modifiers enhance the disorder of the resulting materialsand thus create a greater number and spectrum of catalytically activesites and hydrogen storage sites.

The disordered electrode materials of the '597 patent were formed fromlightweight, low cost elements by any number of techniques, whichassured formation of primarily non-equilibrium metastable phasesresulting in the high energy and power densities and low cost. Theresulting low cost, high energy density disordered material allowed thebatteries to be utilized most advantageously as secondary batteries, butalso as primary batteries.

Tailoring of the local structural and chemical order of the materials ofthe '597 patent was of great importance to achieve the desiredcharacteristics. The improved characteristics of the anodes of the '597patent were accomplished by manipulating the local chemical order andhence the local structural order by the incorporation of selectedmodifier elements into a host matrix to create a desired disorderedmaterial. Disorder permits degrees of freedom, both of type and ofnumber, within a material, which are unavailable in conventionalmaterials. These degrees of freedom dramatically change a materialsphysical, structural, chemical and electronic environment. Thedisordered material of the '597 patent have desired electronicconfigurations which result in a large number of active sites. Thenature and number of storage sites were designed independently from thecatalytically active sites.

Multiorbital modifiers, for example transition elements, provided agreatly increased number of storage sites due to various bondingconfigurations available, thus resulting in an increase in energydensity. The technique of modification especially providesnon-equilibrium materials having varying degrees of disorder providedunique bonding configurations, orbital overlap and hence a spectrum ofbonding sites. Due to the different degrees of orbital overlap and thedisordered structure, an insignificant amount of structuralrearrangement occurs during charge/discharge cycles or rest periodsthere between resulting in long cycle and shelf life.

The improved battery of the '597 patent included electrode materialshaving tailor-made local chemical environments which were designed toyield high electrochemical charging and discharging efficiency and highelectrical charge output. The manipulation of the local chemicalenvironment of the materials was made possible by utilization of a hostmatrix which could, in accordance with the '597 patent, be chemicallymodified with other elements to create a greatly increased density ofelectro-catalytically active sites and hydrogen storage sites.

The disordered materials of the '597 patent were designed to haveunusual electronic configurations, which resulted from the varying3-dimensional interactions of constituent atoms and their variousorbitals. The disorder came from compositional, positional andtranslational relationships of atoms. Selected elements were utilized tofurther modify the disorder by their interaction with these orbitals soas to create the desired local chemical environments.

The internal topology that was generated by these configurations alsoallowed for selective diffusion of atoms and ions. The invention thatwas described in the '597 patent made these materials ideal for thespecified use since one could independently control the type and numberof catalytically active and storage sites. All of the aforementionedproperties made not only an important quantitative difference, butqualitatively changed the materials so that unique new materials ensued.

Disorder can be of an atomic nature in the form of compositional orconfigurational disorder provided throughout the bulk of the material orin numerous regions of the material. The disorder also can be introducedby creating microscopic phases within the material which mimic thecompositional or configurational disorder at the atomic level by virtueof the relationship of one phase to another. For example, disorderedmaterials can be created by introducing microscopic regions of adifferent kind or kinds of crystalline phases, or by introducing regionsof an amorphous phase or phases, regions of an amorphous phase or phasesin addition to regions of a crystalline phase or phases. The interfacesbetween these various phases can provide surfaces which are rich inlocal chemical environments which provide numerous desirable sites forelectrochemical hydrogen storage.

These same principles can be applied within a single structural phase.For example, compositional disorder is introduced into the materialwhich can radically alter the material in a planned manner to achieveimportant improved and unique results, using the Ovshinsky principles ofdisorder on an atomic or microscopic scale.

Additionally, in copending U.S. application Ser. No. 09/524,116, ('116),the disclosure of which is hereby incorporated by reference, Ovshinskyhas employed the principles of atomic engineering to tailor materialswhich uniquely and dramatically advance the fuel cell art. The inventionof '116 application has met a need for materials which allow fuel cellsto startup instantaneously by providing an internal source of fuel, tooperate in a wide range of ambient temperatures to which a fuel cellwill be exposed to under ordinary consumer use and to allow the fuelcell to be run in reverse as an electrolyzer thereby utilizing/storingrecaptured energy. The anodes of the '116 fuel cells are formed fromrelatively inexpensive hydrogen storage materials which are highlycatalytic to the dissociation of molecular hydrogen and the formation ofwater from hydrogen and hydroxyl ions as well as being corrosionresistant to the electrolyte, resistant to contaminant poisoning fromthe reactant stream and capable of working in a wide temperature range.

The next step in the evolution of the fuel cell would be to findsuitable materials to replace the expensive platinum cathode catalystsof conventional fuel cells. It would also be advantageous to provide thecathode with the ability to store chemical energy (possibly in the formof chemically bound oxygen) to assist in the instant startup of the fuelcell as well as recapture energy Thus there is a need within the art forsuch a material. The invention described this application is significantin that it provides the next step in the development of suchelectrochemical cells. With this invention, the cathode can be selectedfrom a broad menu of available possible redox couples. These redoxcouples in addition to providing a store of chemical energy, allow theoperating voltage of the fuel cell to be selected, by judicious choiceof the redox couple used.

SUMMARY OF THE INVENTION

The present invention discloses cathodes utilizing a novel cathodeactive material. When utilized in fuel cell cathodes, the cathode activematerial provides the fuel cell with the ability to start up instantlyand accept recaptured energy such as that of regenerative braking byoperating in reverse as an electrolyzer. The instant startup fuel cellshave increased efficiency and power availability (higher voltage andcurrent) and a dramatic improvement in operating temperature range (−20to 150° C.) The fuel cells of the instant invention also have additionaldegrees of freedom over the fuel cells of the prior art in that thevoltage output of the cell can be tailored and they are capable ofstoring regenerated energy.

The cathodes of the present invention operate through the mechanism ofvalency change reactions which uniquely provide multiple degrees offreedom in selecting the operating voltages available for such fuelcells. Such cathodes provide the fuel cells in which they are used,particularly alkaline fuel cells, with a level of chemical energystorage within the cathode itself. This means that such fuel cells willhave a “buffer” or “charge” available within the cathode at all times.

The cathode in accordance with the present invention comprises a cathodeactive material including a valency change material. The valency changematerial provides the cathode with an oxygen storage capacity. Thevalency change material may be a nickel hydroxide/nickel oxyhydroxideredox couple, a metal/metal oxide redox couple of an element selectedfrom copper, silver, zinc and cadmium, a metal oxide/oxide redox coupleof a metal such as manganese, or a cobalt hydroxide/oxyhydroxide redoxcouple.

The cathode may further include a hydrophobic component such aspolytetrafluoroethylene (PTFE). The hydrophobic component may be a)intimately mixed with the cathode active material, b) graded within thecathode active material, or c) a separate layer within the cathode. Thecathode may further include a current collector extending within thecathode active material. The current collector may comprise anelectrically conductive mesh, grid, foam or expanded metal. The furtherincluding a catalytic carbon component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a stylized schematic depiction of a fuel cell anode used inthe fuel cells of the instant invention;

FIG. 1B is a stylized schematic depiction of an inventive fuel cellcathode used in the fuel cells of the instant invention;

FIG. 2 is a stylized schematic depiction of the instant startup alkalinefuel cell with hydrogen storage anode and oxide couple cathode in apreferred embodiment of the instant invention;

FIG. 3 a is a plot of electrode potential (volts) of the cathode versusthe current density (mA/cm²) for both the redox cathode of the instantinvention and the comparative cathode;

FIG. 3 b is a plot of percentage improvement of the voltage (reductionof polarization of the electrode) of the inventive cathode over thecomparative cathode versus the current density (mA/cm²);

FIG. 4 is a stylized schematic depiction of an energy supply systemincorporating the instant startup alkaline fuel cell of a preferredembodiment of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

The present invention relates to cathodes for fuel cells which operatethrough the mechanism of valency change reactions of redox couples. Themechanism of valency change reactions uniquely provides multiple degreesof freedom in selecting the operating voltages available for such fuelcells by selecting from the many variable and reversible redox couplesavailable. Such cathodes, or cathodes, provide the fuel cells in whichthey are used, particularly alkaline fuel cells, with a level ofelectrochemical energy storage via a change in valency state within thecathode itself. This means that such fuel cells will have a “buffer” or“charge” of reactant available within the cathode at all times which,particularly combined with hydrogen storage anodes described incopending U.S. application Ser. No. 09/524,116 (the disclosure of whichis hereby incorporated by reference), yield instant start fuel cells ingeneral and more specifically to instant start alkaline fuel cells. Suchfuel cells have a built in reserve of hydrogen within the anode andcathode reactant (possibly oxygen) in the cathode for instant startup(discussed herein below), and have the ability to accept the energy ofregenerative braking by acting as an electrolyzer (also discussed hereinbelow). The fuel cell has increased efficiency and increased powercapabilities as compared with conventional fuel cells of the prior art,while dramatically increasing the operating temperature range of thecell (−20 to 150° C.) The fuel cell is easy to assemble and has theadvantage of utilizing proven, low cost production techniques.

The present invention also relates to fuel cell anodes and cathodes, andan energy supply system incorporating the present fuel cell. The fuelcell anode includes materials which have inherent catalytic activity aswell as hydrogen storage capacity. The cathode and anode materials donot include any noble metals, and are therefore inherently low cost. Thecathode and anode materials are robust and long-lived, being resistantto poisoning. The anode does not utilize the carbon substrates of theprior art. While a detailed discussion of the instant electrodes andtheir utilization in an alkaline fuel cell is described herein below, itshould be noted that the concepts of the instant invention can beapplied to other types of fuel cells (e.g. P.E.M. fuel cells ormetal-air cells).

In general, for such fuel cell cathodes, oxygen is generally availableto the cathode on a continuously-supplied basis on one side of thereofwhere the catalytically active material converts the molecular oxygeninto atomic oxygen which then migrates through the electrode and isreduced at the electrolyte interface of the cathode to form hydroxylions. In prior art cathodes, no storage of reactant occurs. That isoxygen travels directly through the active materials and reacts at theelectrolyte interface. In the cathodes of the instant invention, oxygenis stored in the cathode via a change in valency state within thereversible redox couples, and is then available, at the electrolyteinterface of the cathode. Available electrons will then be generatedthrough the electrochemical reaction with the fuel. Thus the fuel cellwill provide a constant supply of electricity at voltages based on thevalency change of the reversible redox couple being used (e.g. a metaland its oxide). Additionally, this added benefit may be obtained via achange in valency state in redox couples other than a metal and itsoxidized form. An example of this is the redox couple of nickelhydroxide/nickel oxyhydroxide or cobalt hydroxide/oxyhydroxide. Suchvalency changes may also occur between two different oxides of a metal,such as manganese or tin. In these types of systems, the electrochemicalcell will provide a potential whose theoretical voltage limit is the sumof the anode and cathode reactions. Certainly the theoretical limit ofvoltage available is modified or limited by other considerations, whichmay include the internal resistance of the electrodes and the completefuel cell system.

This invention specifically relates to a fuel cell cathode comprising acathode active material capable of reversibly storing energy through avalency change mechanism of a redox couple. The cathode active materialmay have a first surface region situated to be exposed to molecularoxygen. The first surface region including a catalytically actingcomponent promoting the absorption of molecular oxygen through saidfirst surface region and conversion thereof into atomic oxygen. Theactive material also includes a redox couple material (e.g. a metal)which is thereafter chemically charged by reaction with the atomicoxygen resulting in a valency change. The fuel cell cathode alsoincludes a second surface region situated to be exposed to a fuel cellelectrolyte. The second surface region includes a catalytic componentpromoting the valency change reactions between the redox active materialand the electrolyte. The cathode may also include a hydrophobiccomponent positioned between the first and second surface regions. Sucha fuel cell cathode will display favorable voltage potential overconventional prior art cathodes.

The fuel cell cathodes of this invention may utilize valency changeredox couples, particularly metal/oxides couples of metals selected fromcopper, silver, zinc, cobalt and cadmium, metal oxide/oxide couples ofmetals selected from manganese or tin, or a nickel hydroxide/nickeloxyhydroxide couple or a cobalt hydroxide/oxyhydroxide couple.

The fuel cell cathodes of the instant invention also include a catalyticmaterial which promotes and speeds the dissociation of molecular oxygeninto atomic oxygen (which reacts with the redox couple). A particularlyuseful catalyst is carbon. As discussed herein below this carbon shouldbe very porous and may be electrically conductive.

The cathode also needs a barrier means to isolate the electrolyte, orwet, side of the cathode from the gaseous, or dry, side of the cathode.A beneficial means of accomplishing this is by inclusion of ahydrophobic component comprising a halogenated organic compound,particularly polytetrafluoroethylene (PTFE) within the electrode.

These fuel cell cathodes, may also include a current collector orcurrent collecting system extending within said active material. Asdiscussed herein below, the current collector may comprise anelectrically conductive mesh, grid, foam or expanded metal. The choiceof such collection systems may be made according to electrodemanufacturing or production system needs.

Fuel cells of the instant invention using cathodes with valency changeredox couples, particularly in combination with the hydrogen storageanodes of the '116 application provided the ability to recapture reverseelectrical power flow from an external circuit into said fuel cell,electrolytically producing hydrogen and oxygen which are absorbed andstored through the mechanism of valency change reactions within theredox couple in the cathode and the hydrogen storage material in theanode.

Such fuel cells may, as a system, further comprise an electrolyteconditioning means for conditioning the electrolyte. This electrolyteconditioning system will not only adjust the temperature of theelectrolyte (for optimal fuel cell performance) but will also removewater from the electrolyte. The water removal is necessary because wateris produced as a by-product of the fuel cell's electrochemicalcombustion. This water, if not removed would dilute the electrolyte,thus impeding the optimal performance of the fuel cell.

These fuel cells will further include, as a system, a hydrogen supplysource including means for continuously supplying fuel, particularlymolecular hydrogen, to the anode's first surface region; an oxygensupply source which includes means for continuously supplying molecularoxygen to the cathode's first surface region; and an electrolyteconditioning system which includes means for continuously conditioningthe electrolyte, thereby enabling continuous operation of the fuel cellas an electrical power source.

Numerous valency change redox couples exist and may be used to form thecathode of this invention. When such couples are used, cyclingtransition from one valency state (the oxidized form) to another valencystate (the reduced form) is accomplished repeatedly and continuously.From a practical point of view, the ability to withstand such cycling ispreferred. While not wishing to be bound by theory, the inventorsbelieve that the equations representing some of the many availablereactions for the oxygen side of the fuel cell are presented below.Co⁺²⇄Co⁺³ (Valency level 2 to a valency level 3)Co(OH)₂+OH⁻→CoOOH+H₂O+e ⁻  (1)Co⁺²⇄Co⁺⁴ (Valency level 2 to a valency level 4)Co(OH)₂+2OH⁻→Co(OH)₄+2e ⁻Co(OH)₄⇄CoO₂+2H₂O  (2)Ni⁺²⇄Ni⁺³ (Valency level 2 to valency level 3)Ni(OH)₂+OH⁻→NiOOH+H₂O+e ⁻  (3)Ni⁺²⇄Ni⁺⁴ (Valency level 2 to valency level 4)Ni(OH)₂+2OH⁻→Ni(OH)₄+2e ⁻Ni(OH)₄→NiO₂+2H₂O  (4)Ag⇄Ag⁺ (Valency level 0 to valency level 1)2Ag+2OH⁻→Ag₂O+H₂O+e ⁻  (5)Ag⇄Ag⁺² (Valency level 0 to valency level 2)Ag+2OH⁻→AgO+H₂O+2e ⁻  (6)Cu⇄Cu⁺² (Valency level 0 to valency level 2)Cu+2OH⁻→CuO+H₂O+2e ⁻  (7)(Ni/Ag)⁺²⇄(Ni/Ag)  (8)(Ni/Fe) oxide⁺²⇄(Ni/Fe)oxide⁺³  (9)Mn⁺²⇄Mn⁺³→Mn⁺⁷  (10)Sn⁺²⇄Sn⁺⁴  (11)

Groups 8, 9, 10, and 11 are comprised of multiple elements havingmultiple valency states. The multiple valency states may createdifficulty in predicting which reaction is predominant in each grouping.

As noted earlier, the previous sets of reactions provide a few exemplaryvalency change reactions which will be useful for the air or oxygen sideof fuel cells using the cathodes of this invention. These examples areprovided simply to demonstrate useful couples; the list certainly is notexhaustive, nor is it intended to be so. Many other valency change redoxcouples are available and will have useful application in the inventiveoxygen-side electrodes which are, in turn, useful in the describedinventive fuel cells.

Quantifying the useful benefits of a few of these couples it should benoted that use of the copper/copper oxide couple will yield voltage ofabout 0.8 v per cell; silver/silver (+2 oxidation state) oxide willyield voltage of about 0.9 v per cell; nickel oxyhydroxide/nickelhydroxide will yield voltage of about 1 v per cell. It should also beconsidered that there are a number of complex oxides which will yielddiffering cell voltages which expands the available working voltageseven further. Nickel ferrate (NiFeO₄) is one such oxide whose complex isavailable to be used and whose voltage contribution would be about 1volt. This and other “mixed” oxide complexes provide other usefulvoltage opportunities as part of this invention. The nickeloxyhydroxide/hydroxide which was previously discussed is, effectively,another complex oxide system. Some of these offer unique multi-stepreactions which may be advantageously applied in the practice of thisinvention.

At the cathode, the oxygen, water, and electrons react in the presenceof the cathode active material to reduce the oxygen and form hydroxylions (OH⁻):O₂+2H₂O+4e ⁻→4OH⁻.The flow of electrons is utilized to provide electrical energy for aload externally connected to the anode and cathode. That load isavailable to be filled by any number of needs including, but not limitedto, powering motive vehicles, lighting devices, heating or coolingdevices, power tools, entertainment devices, and otherelectricity-consuming devices too numerous to mention.

In a fuel cell, the cathodes just described (employing any of the manyvalency change redox couples) are used in conjunction with an anode orhydrogen electrode. While any functional hydrogen electrode may be usedwith the inventive cathodes, preferred embodiments of the fuel cells ofthis invention will include anodes employing hydrogen storage alloyactive materials. It should be noted that the preferred anode catalystof the alkaline fuel cell is required to do more than catalyze thereaction of H⁺ ions with OH⁻ ions to produce water. Initially the anodemust catalyze and accelerate the formation of H⁺ ions and e⁻ from H₂.This occurs via formation of atomic hydrogen from molecular hydrogen.The overall reaction can be seen as (where M is the hydrogen storageanode active alloy material):M+H₂ →M . . . H→MH→M+H ⁺ +e ⁻.That is, molecular hydrogen (H₂) is converted to adsorbed atomichydrogen (M . . . H) onto the surface of the anode. This adsorbedhydrogen is very quickly converted to a metal hydride (MH) in the bulkof the hydrogen storage alloy. This hydride material is then convertedto ionic H⁺ releasing an electron e⁻. The ionic hydrogen reacts with ahydroxyl ion in the electrolyte to produce water and the electron isreleased into the external load circuit. Thus the anode catalyst mustnot only efficiently catalyze the formation of water at the electrolyteinterface, but must also efficiently dissociate molecular hydrogen intoionic hydrogen. Using conventional anode material, the dissociatedhydrogen is transitional and the hydrogen atoms can easily recombine toform hydrogen if they are not used very quickly in the oxidationreaction. With hydrogen storage anode materials, hydrogen is trapped inhydride form as soon as hydrides are created. The hydrogen, aselectrochemically released into the electrolyte, are then used as neededto provide the fuel cell's electrical power output.

In addition to being catalytically efficient on both interfaces, thecatalytic material must be resistant to corrosion by the alkalineelectrolyte. Without such corrosion resistance, the electrode wouldquickly succumb to the harsh environment and the cell would quickly loseefficiency and die.

One prior art fuel cell anode catalyst is platinum. Platinum, despiteits good catalytic properties, is not very suitable for wide scalecommercial use as a catalyst for fuel cell anodes, because of its veryhigh cost. Also, noble metal catalysts like platinum cannot withstandcontamination by impurities normally contained in the hydrogen fuelstream. These impurities can include carbon monoxide (which may bepresent in hydrogen fuel) or contaminants contained in the electrolytesuch as the impurities normally contained in untreated water such ascalcium, magnesium, iron, and copper.

The above contaminants can cause what is commonly referred to as a“poisoning” effect. Poisoning occurs where the catalytically activesites of the material become inactivated by poisonous species invariablycontained in the fuel cell. Once the catalytically active sites areinactivated, they are no longer available for acting as catalysts forefficient hydrogen oxidation reaction at the anode. The catalyticefficiency of the anode therefore is reduced since the overall number ofavailable catalytically active sites is significantly lowered bypoisoning. In addition, the decrease in catalytic activity results inincreased overvoltage at the anode making the cell much less efficientresulting in an increase to the operating costs. Overvoltage is thedifference between the electrode potential and it's equilibrium value,the physical meaning of over-voltage is the voltage required to overcomethe resistance to the passage of current at the surface of the anode(charge transfer resistance). The overvoltage represents an undesirableenergy loss which adds to the operating costs of the fuel cell.

Without intending to limit the true scope of this invention, but ratherfor the purpose of explanation and making the current invention moreunderstandable, explanatory drawings are provided. FIGS. 1A and 1B arestylized schematic depictions of a fuel cell storage electrodes 1 a and1 c (“a” designates anode and “c” designates cathode). The anode 1 apreferably comprises a hydrogen storage active material and the cathodepreferably comprises a cathode active material including a valencychange redox couple. The electrode body includes, in a preferredembodiment a hydrophobic component 2 a (anode) and 2 c (cathode). Thehydrophobic component may be polytetrafluoroethylene (PTFE). Theelectrodes also include either a region comprising hydrogen storageactive material 3 a for the anode, or a region comprising at least onevalency change redox couple 3 c for the cathode. While FIGS. 1A and 1Bshow the hydrophobic component 2 a, 2 c and the active electrodematerial component 3 a, 3 c as separate layers of material within theelectrodes 1 a, 1 c, they may also be intimately mixed into a singlematerial or graded throughout the active material. The electrodes 1 a, 1c also include a substrate component 4 a (anode) or 4 c (cathode), whichat least acts as a current collector, but may also provide a supportfunction. This substrate component is discussed herein below.

The electrodes 1 a, 1 c have two surfaces 5 a (anode) or 5 c (cathode),and 6 a (anode) or 6 c (cathode). One surface of each electrode 5 a, 5 cis adjacent a reactant (i.e. hydrogen or oxygen) which is usefullysupplied by an inlet mechanism when incorporated into the fuel cell,while the other surface 6 a, 6 c is adjacent to the electrolyte (whichin a preferred embodiment will be an aqueous alkaline electrolyte). Asstated above, the hydrophobic (PTFE) component 2 a, 2 c is either alayer within the electrodes or is intimately mixed with the activematerial 3 a, 3 c. In either case, the purpose of the hydrophobic (PTFE)material is to act as a water barrier, preventing electrolyte or itsdiluent from escaping from the fuel cell, while at the same time,allowing either the fuel, preferably hydrogen (in the case of the anode)or the oxygen (in the case of the cathode) to pass from the sourcethereof to the electrode active material 3 a, 3 c. Thus, a portion ofthe electrode, surface 6 a, 6 c (and somewhat interiorly from thesurface) is in contact with the electrolyte and acts to oxidize(providing electrons) the fuel, preferably hydrogen in the anode case orreduce (gaining electrons) the oxidizer, preferably oxygen in thecathode case, while the remainder of the electrode material (includingsurface 5 a, 5 c) provides for dissociation of molecular hydrogen oroxygen and storage of the dissociated fuel (anode) or oxidizer (cathode)for later reaction at surface 6 a, 6 c.

In the drawings, the anode active material is a material, such as aplatinum based active material or a hydrogen storage material. Thepreferable hydrogen storage alloy is one which can reversibly absorb andrelease hydrogen irrespective of the hydrogen storage capacity and has afast hydrogenation reaction rate, good stability in the electrolyte, anda long shelf-life. It should be noted that, by hydrogen storagecapacity, it is meant that the material stores hydrogen in a stableform, in some nonzero amount higher than mere trace amounts. Preferredmaterials will store about 0.1 weight % hydrogen or more. Preferably,the alloys include, for example, rare-earth/Misch metallic alloys,zirconium, and/or titanium alloys or mixtures thereof. The anodematerial may even be layered such that the material on the hydrogeninput surface 5 a is formed from a material which has been specificallydesigned to be highly catalytic to the dissociation of molecularhydrogen into atomic hydrogen, while the material on electrolyteinterface surface 6 a is designed to be highly catalytic to theformation of water from hydrogen and hydroxyl ions.

For the cathode, the active material is a composite of a selectedvalency change redox couple providing for oxygen storage via a valencychange and an additional catalytic material. Some preferable valencychange redox couples are discussed herein above. As general preferences,the valency change redox couple should reversibly absorb and releaseoxygen irrespective of the oxygen storage capacity and have a fastoxidation reaction rate, good stability in the electrolyte, and a longshelf-life. It should be noted that, by oxygen storage capacity, it ismeant that the material stores oxygen in a stable form via a valencychange reaction, in some nonzero amount higher than mere trace amounts.

In either case, for either electrode, the electrode material may belayered such that the material on the fuel, or oxidizer, input surface 5a, 5 c is formed from a material which has been specifically designed tobe highly catalytic to the dissociation of either the fuel or theoxidizer, while the material on electrolyte interface surface 6 a, 6 cis designed to be highly catalytic to the formation of water (anode) orhydroxyl ions (cathode). In addition to having exceptional catalyticcapabilities, the materials also have outstanding corrosion resistancetoward the electrolyte of the fuel cell.

In use, the anode (hydrogen electrode) alloy materials act as 1) amolecular hydrogen decomposition catalyst throughout the bulk of theanode; 2) as a water formation catalyst, forming water from hydrogen andhydroxyl ions (from the aqueous alkaline electrolyte) at surface 6 ofthe anode; and 3) as an internal hydrogen storage buffer to insure thata ready supply of hydrogen ions is always available at surface 6 (thiscapability is useful in situations such as fuel cell startup andregenerative energy recapture, discussed herein below).

Specific alloys useful as the anode material are alloys that containenriched catalytic nickel regions of 50–70 Angstroms in diameterdistributed throughout the oxide interface which vary in proximity from2–300 Angstroms preferably 50–100 Angstroms, from region to region. As aresult of these nickel regions, the materials exhibit significantcatalysis and conductivity. The density of Ni regions in the alloy ofthe '591 patent provides powder particles having an enriched Ni surface.The most preferred alloys having enriched Ni regions are alloys havingthe following composition:

-   (Base Alloy)_(a)Co_(b)Mn_(c)Fe_(d)Sn_(e)    where the Base Alloy comprises 0.1 to 60 atomic percent Ti, 0.1 to    40 atomic percent Zr, 0 to 60 atomic percent V, 0.1 to 57 atomic    percent Ni, and 0 to 56 atomic percent Cr; b is 0 to 7.5 atomic    percent; c is 13 to 17 atomic percent; d is 0 to 3.5 atomic percent;    e is 0 to 1.5 atomic percent; and a+b+c+d+e=100 atomic percent.

The substrate component 4 a, 4 c acts as an electrical conductor and mayusefully also act as a support means. For example, if a powderedelectrically conductive material, such as nickel, nickel alloy, copper,copper alloy or carbon, is mixed into the active material 3 a, 3 c thenthe material acts as an electrically conductive materials, but does notprovide any support for the electrode materials per se.

It is preferable that the substrate component act as both an electricalconductor and a support structure. The electrode may be formed bypressing active material into a porous metal substrate. The conductivityof the electrode can be increased by increasing the conductivity of theelectrode's porous metal substrate. Generally the porous metal substrateincludes, but is not limited to, meshes, grid, matte, foil, foam, plate,and expanded metal. Preferably, the porous metal substrate used for theelectrode is a mesh, grid, foam, or expanded metal. The substrate may beformed from any material which is electrically conductive and resistantto corrosion or chemical attack by the electrolyte. Nickel or nickelalloy is a very good material, but for high power applications it may betoo resistive. Thus when high power is required, the substrate is formedfrom copper, copper-plated nickel, or a copper-nickel alloy, as taughtby U.S. Pat. No. 5,856,047 (Venkatesan, et al.) and U.S. Pat. No.5,851,698 (Reichman et al.), the disclosures of which are herebyincorporated by reference. As used herein, “copper” refers to eitherpure copper or an alloy of copper, and “nickel” refers to either purenickel or an alloy of nickel. Using copper to form the porous metalsubstrate of the electrode has several important advantages. Copper isan excellent electrical conductor. Hence, its use as a substratematerial decreases the resistance of the anode. This decreases theamount of fuel cell power wasted due to internal dissipation, andthereby provides a fuel cell having increased output power. Copper isalso a malleable metal. Increased substrate malleability allows thesubstrate to more reliably hold the active hydrogen storage materialthat is compressed onto the substrate surface. This lessens the need tosinter the electrode after the active material has been compressed ontothe substrate, thereby simplifying and reducing the cost of the anodemanufacturing process.

The cathode contains an active material component which is catalytic tothe dissociation of molecular oxygen into atomic oxygen and/or catalyticto the formation of hydroxyl ions (OH⁻) and hydrogen from water,corrosion resistant to the electrolyte, and resistant to poisoning.

The cathode is formed in much the same manner as the anode or may beformed in a manner similar to conventional cathodes which use platinumcatalysts, but the valency change redox couple materials described aboveare substituted for the platinum. The valency change redox couple isfinely divided and disbursed throughout a porous carbon material. Thecarbon material may be in the form of a powder, matte, foam, grid ormesh. The cathode may or may not have a conductive substrate as needed.If used the substrate can be as described in relation to the anode.

When the instant fuel cell is run in reverse, as an electrolyzer, duringan energy recapture process such as regenerative braking, water iselectrolyzed into hydrogen and oxygen. That is, when electric poweredvehicles are used in stop and go mode in inner cities, regenerativebraking systems can recapture kinetic energy, and convert it toelectrical energy. In this mode, the electric motors reverse their rolesand become generators using up the kinetic energy of the motion. Thiscauses a spike of current which amounts to about 10% of the normaloperating load. A conventional fuel cell (alkaline or PEM) cannot acceptsuch surges. This feedback of energy would cause rapid hydrogen andoxygen evolution which would cause the catalysts to lose their integrityand adhesion thereby undermining the overall system performance.

In the inventive fuel cell, this will not be a problem, because thehydrogen storage anode and the valency change redox couple cathode willtake the surge current and become charged with the produced hydrogen oroxygen respectively.

It should be noted that the anode and cathode active materials of theinstant invention are robust and very resistant to poisoning. This istrue because the increased number of catalytically active sites of thesematerials not only increases catalytic activity, but enables thematerials to be more resistant to poisoning, because with materials ofthe present invention numerous catalytically active sites can besacrificed to the effects of poisonous species while a large number ofnon-poisoned sites still remain active to provide the desired catalysis.Also, some of the poisons are inactivated by being bonded to other siteswithout effecting the active sites.

FIG. 2 is a stylized schematic depiction of an alkaline fuel cell 7incorporating the electrodes 1 a, 1 c (“a” designates anode and “c”designates cathode) of the instant invention. The fuel cell 7 consistsof three general sections: 1) an anode section, which includes the anode1 a and a hydrogen supply compartment 8; 2) the electrolyte compartment11; and 3) the cathode section, which includes the cathode 1 c and theoxygen (air) supply compartment 10.

In the anode section, hydrogen or hydrogen containing gas mixtures issupplied under pressure to the hydrogen supply compartment 8 throughhydrogen inlet 12. Hydrogen is then absorbed through surface 5 a intothe anode 1 a. The absorbed hydrogen is catalytically broken down by theanode active material into atomic hydrogen which is stored in thehydrogen storage material as a hydride, and then finally reacts atsurface 6 a with hydroxyl ions to form water. It should be noted thatthe heat of hydride formation helps to warm the fuel cell to it'soptimal operating temperature. Any unabsorbed hydrogen and othercontaminant gases or water vapor in the hydrogen supply are ventedthrough outlet 13. The gases that are vented may be recycled if enoughhydrogen is present to warrant recovery. Otherwise the hydrogen may beused to provide a source of thermal energy if needed for othercomponents such as a hydride bed hydrogen storage tank.

The electrolyte compartment 11 holds (in this specific example) anaqueous alkaline electrolyte in intimate contact with the anode 1 a andthe cathode 1 c. The alkaline solution is well known in the art and istypically a potassium hydroxide solution. The electrolyte provideshydroxyl ions which react with hydrogen ions at surface 6 a of the anode1 a and water molecules which react with oxygen ions at surface 6 c ofthe cathode 1 c. The electrolyte is circulated through compartment 11via inlet 14 and outlet 15 (in alternative embodiments, the electrolytemay be deliberately immobilized as by jelling, etc.) The circulatedelectrolyte may be externally heated or cooled as necessary, and theconcentration of the electrolyte can be adjusted (as via wicking, etc.)as needed to compensate for the water produced by the cell and anylosses due to evaporation of water through the electrodes. Systems forconditioning the fuel cell electrolyte are well known in the art andneed not be further described in detail herein.

In the cathode section, oxygen, air, or some other oxygen containinggaseous mixture is supplied to the oxygen supply compartment 10 throughoxygen inlet 18. Oxygen is then absorbed through surface 5 c into thecathode 1 c. The absorbed oxygen is catalytically broken down by thecathode active material into atomic oxygen, which finally reacts atsurface 6 c (via the valency change mechanism of the redox couple) withwater molecules to form hydroxyl ions. Any unabsorbed oxygen and othergases in the feed (e.g. nitrogen, carbon dioxide, etc.) or water vaporin the oxygen supply are vented through outlet 19.

EXAMPLE

Production of a hydrogen storage anode (used in both the inventive fuelcell and the control cell) is described as follows. All percentagesgiven throughout this example are in weight percent, unless otherwisenoted. A mixture containing about 90% of a Mischmetal nickel alloy(having an approximate composition of 20.7% La, 8.5% Ce, 1.0% Pr. 2.9%Nd, 49.9% Ni, 10.6% Co, 4.6% Mn, 1.8% Al) and about 10%polytetrafluoroethylene (PTFE) was made into a paste using isopropylalcohol. This paste was applied into an Inco Corporation nickel foamhaving a of density of about 500 g/m² (with a previously welded nickeltab used as a current collector). This foam acts as the substrate andelectrical collector for the electrode. After drying at 50–60° C., theanode was compacted using a roll mill to a final thickness of 0.020 to0.030 inches.

The control sample cathode (oxygen) electrode was created as follows.First, a mixture of Vulcan XC-72 carbon (Trademark of Cabot Corp.) andPTFE was prepared with an approximate PTFE content of 20–30%. Nickelfoam of the type used above in the anode production was used as asubstrate. A paste (paste A) of the Vulcan XC-72 carbon/PTFE mixture wascreated using sufficient isopropyl alcohol to produce a workable paste.Paste A was then applied into one side (the electrode/gas interfaceside) of the foam substrate. A second paste (paste B), consisting of amixture of approximately of 40–60% of the Vulcan XC-72 carbon/PTFEmixture and a high surface area carbon (Black Pearls 2000, Trademark ofCabot Corp.) was created, again using sufficient isopropyl alcohol toproduce a workable paste. Paste B was applied into the other side (theelectrode/electrolyte interface side) of the foam. After drying theelectrode at 60–100° C., it was compacted to final thickness of 0.030 to0.040 inches by applying even pressure of 1 to 3 tons/cm².

The inventive electrode was created in a similar manner as thecomparative electrode except that 10% Aldrich silver oxide was added topaste B. The inventive cathode contains only about 0.11 grams of activesilver oxide redox material. This amount of silver oxide has anelectrochemical capacity of about 40 mAh. At a typical discharge rate of100 mA/sq.cm, the electrode would be discharged at a current of 1A. Atthis current, the electrode should be fully discharged in 2.5 minutes ifthere is no continuous regeneration of the active ingredients. Also thecell voltage, which includes all polarizations, should reflect a highervalue if oxygen reduction were occurring by a redox mechanism as opposedto the conventional mechanism.

Fuel cells were created using the same anodes and respectively eitherthe control cathode or the inventive cathode. These fuel cells includeda 60 g/m² polypropylene separator from Daiwabo Corporation, and employedconventional KOH/LiOH alkaline battery electrolyte which was jelledusing 3% carboxymethylcellulose. The cells were run using purifiedhydrogen as the fuel and air as the source of oxygen.

FIG. 3 a is a plot of electrode potential (volts) of the cathode versusthe current density (mA/cm²) for both the inventive valency change redoxcouple cathode (♦ symbol) and the comparative cathode (▪ symbol). Eachdata point represents 5 minutes of discharge at that particular currentdensity. Thus as can be seen, the electrode potential for the inventivecathode is always higher than that of the control sample (at usefulcurrent densities) and as the current density increases (i.e. higherpower) the voltage of the control sample drops off much more rapidlythan that of the inventive cathode (which drops only slightly bycomparison) FIG. 3 b is a plot of percentage improvement of the voltage(reduction of polarization of the electrode) of the inventive cathodeover the comparative cathode versus the current density (mA/cm²). As maybe seen from this graph, at useful current densities, the improvement inthe polarization of the inventive electrode is anywhere from 30% to 50%over that of the comparative cathode. Thus, FIGS. 3 a and 3 b show thatthe cell is fully capable of operating for longer than 2.5 minutes (thecapacity base of only the silver oxide in the cathode) and at a highervoltage than the comparative cathode. Therefore, it is apparent thatcontinuous replenishment of oxygen into the silver oxide redox couplevia a change in the valency state of the redox couple by the suppliedair is being accomplished.

It should be noted that cathodes containing in the range of 1–20% byweight of silver oxide (in paste B) were produced. Cathodes having loweramounts of silver oxide than the 10% in the cathode of the example (i.e.in the 1% range) showed the same effects, although somewhat diminished.Cathodes produced with higher than the 10% silver oxide of the examplecathode (i.e. about 20%) showed no increased effect over the samplecathode. Thus, the effective range appears bounded by a lower limit ofabout 0.5% silver oxide. The upper limit of silver oxide inclusion seemsto only be bounded by factors such as cost and the need for carbon tocatalyze the reaction at the electrode/electrolyte interface. This rangelimit, determined by empirical means, applies only to silver, and otherredox couples will have their own limits on the range of inclusion whichmay be determined by similar simple experimental trials.

FIG. 4 is a stylized schematic depiction of an energy supply systemincorporating the alkaline fuel cell 7 of the instant invention. Theenergy supply system also includes a source of hydrogen 20. The sourcemay be of any known type, such as a hydride bed storage system, acompressed hydrogen storage tank, a liquid hydrogen storage tank, or ahydrocarbon fuel reformer. The preferred source is a metal hydridestorage system. The hydrogen from the source 20 is transported to thefuel cell 7 via input line 21, and excess gases are vented throughoutput line 22. A portion of the gases from output line 22 may berecycled to input line 21 through recycle line 32. The energy supplysystem also includes a source of oxygen, which is preferably air. Theair is drawn into line 33 and then can be passed through a carbondioxide scrubber 23. The air is then transported to the fuel cell 7 viainput line 24. Excess air and unused gases are vented through outputline 25. Since this gas stream contains no harmful gases, it may bevented to the environment directly.

The energy supply system also includes an electrolyte recirculationsystem. The electrolyte from the fuel cell 7 is removed through outputline 28 and sent to an electrolyte conditioner 26. The electrolyteconditioner 26 heats or cools the electrolyte as needed and removes/addswater as necessary. The conditioned electrolyte is then returned to thefuel cell 7 via input line 27.

Finally the energy supply system includes electrical leads 29 and 30which supply electricity from the fuel cell 7 to a load 31. The load canbe any device requiring power, but particularly contemplated is thepower and drive systems of an automobile.

The instant fuel cell and energy supply systems incorporating it areparticularly useful for applications in which instant start and energyrecapture are requirements thereof, such as for example in powering avehicle. For instance, in consumer vehicle use, a fuel cell that has thebuilt in hydrogen and oxygen storage of the instant invention has theadvantage of being able to start producing energy instantly from thereactants stored in it's electrodes. Thus, there is no lag time whilewaiting for hydrogen to be supplied from external sources. Additionally,because hydrogen and oxygen can be adsorbed and stored in the respectiveelectrode materials of the fuel cell, energy recapture can be achievedas well. Therefore, activities such as regenerative braking, etc., canbe performed without the need for an battery external to the fuel cellbecause any reactants produced by running the fuel cell in reverse willbe stored in the electrodes of the fuel cell. Therefore, in essence,fuel cells employing the instant active electrode materials are theequivalent of a fuel cell combined with a battery. In such a systememploying the valency change redox couples, oxygen is able to be storedwithin the electrode via a change in the valency state of the redoxcouple to a significant degree. Such couples may be a metal/metal oxidecouple, a hydroxide/oxyhydroxide couple, a metal oxide/oxide couple, orcombinations thereof.

The novel electrochemical cell of the present invention also enables thepractice of the method of the invention which, in one embodimentthereof, comprises the indirect and continuous introduction of both thefuel, preferably hydrogen, and the reactant which oxidizes the fuel,preferably oxygen, for the continuous operation of the electrochemicalcell as a fuel cell. That is, the hydrogen is, during operation,continuously introduced through a catalytic region in the negativeelectrode and continuously stored as a hydride in a region of materialin the negative electrode which is capable of reversibly storing andreleasing hydrogen. Simultaneously, hydrogen is electrochemicallyreleased from the electrolyte side of the negative electrode toparticipate in the cell reaction process while a continuous supply ofhydrogen at the gas side is stored within the anode replacing thehydrogen reacted at the electrolyte side.

At the same time oxygen is continuously introduced at the gas side ofthe positive electrode through a catalytic region and chemically storedvia a valency change mechanism as a material in the form of the chargedstate of an oxide couple which participates in the cell reaction.Simultaneously with the introduction and chemical storage of the oxygenas just explained the material of the valency change redox couple whichis in the charged state participates in the cell reaction to generateelectrical power. Thus an electrochemical cell is continuously operatedthrough the supply to the gas side, storage within, and release from theelectrolyte side of, the oxidant so that operation as a fuel cell isenabled. The unique method of the invention of operation of anelectrochemical cell as a fuel cell is thus made possible. In thesituations in which the fuel cell is run “backwards” or as anelectrolyzer to recapture and store energy, such as for example, duringregenerative braking, the operating nature as described earlier wouldnot be considered to be disruptive to “continuous” operation.

While there have been described what are believed to be the preferredembodiments of the present invention, those skilled in the art willrecognize that other and further changes and modifications may be madethereto without departing from the spirit of the invention, and it isintended to claim all such changes and modifications as fall within thetrue scope of the invention.

1. In a electrochemical cell, a cathode comprising: a cathode activematerial including a valency change material for storing and supplyingoxygen via a change in the valency state of said valency changematerial.
 2. The cathode according to claim 1, wherein said valencychange material is a nickel hydroxide/nickel oxyhydroxide redox couple.3. The cathode according to claim 1, wherein said valency changematerial comprises a metal/metal oxide redox couple of an elementselected from the group consisting of copper, silver, zinc and cadmium.4. The cathode according to claim 1, wherein said valency changematerial comprises a metal oxide/oxide redox couple of a metal selectedfrom tin or manganese.
 5. The cathode according to claim 1, wherein saidvalency change material comprises a cobalt hydroxide/oxyhydroxide redoxcouple.
 6. The cathode of claim 1, further including a hydrophobiccomponent.
 7. The cathode of claim 6, wherein said hydrophobic componentcomprises polytetrafluoroethylene.
 8. The cathode of claim 7, whereinsaid polytetrafluoroethylene is at least one of: a) intimately mixedwith said cathode active material; b) graded within said cathode activematerial; or c) a separate layer within said cathode.
 9. The cathode ofclaim 1, further including a current collector extending within saidactive material.
 10. The cathode of claim 9 wherein said currentcollector comprises an electrically conductive mesh, grid, foam orexpanded metal.
 11. The cathode of claim 1, further including acatalytic carbon component.
 12. A cathode active material for a cathodecomprising: a valency change material for storing and supplying oxygenvia a change in valency during use of said cathode.
 13. The cathodeactive material according to claim 12, wherein said valency changematerial is a nickel hydroxide/nickel oxyhydroxide redox couple.
 14. Thecathode active material according to claim 12, wherein said valencychange material comprises a metal/metal oxide redox couple of an elementselected from the group consisting of copper, silver, zinc and cadmium.15. The cathode active material according to claim 12, wherein saidvalency change material comprises a metal oxide/oxide redox couple of ametal selected from tin or manganese.
 16. The cathode active materialaccording to claim 12, wherein said valency change material comprises acobalt hydroxide/oxyhydroxide redox couple.